There are numerous instances where industrial machinery would be hazardous to personnel if started when personnel were located too close to such machinery. Particularly in the coal mining industry, there are elongated conveyor belts, the starting controls for which may be so located that the operator can not see the entire belt from the control position. This is merely one example of power driven machinery which need some sort of automatic warning system to alert workmen to the fact that such machinery is about to be started. With the current emphasis on industrial safety and adequate and interlocked alarm system for use in conjunction with power driven industrial machinery is a necessity both practically and to comply with Federal laws.